Axcelis Technologies, assignee of the present invention, designs and sells products for treatment of workpieces such as silicon wafers during integrated circuit fabrication. Ion implanters create an ion beam that modifies the physical properties of workpieces such as silicon wafers that are placed into the ion beam. This process can be used, for example, to dope the silicon from which the untreated wafer is made to change the properties of the semiconductor material. Controlled use of masking with resist materials prior to ion implantation as well as layering of different dopant patterns within the wafer produce an integrated circuit for use in one of a many applications.
Ion implanters typically include an ion source for producing a plasma from gaseous feed material or from vapor from a solid or liquid feed material. An ion beam is extracted from the source plasma by creating an electric field between the source plasma and another electrode.
After exiting the source the ion beam traverses a region through which the beam is shaped and accelerated to a desired energy before the beam enters an implantation chamber where the ions of the beam impact one or more wafer workpieces. Operation of an ion implanter results in the production of certain contaminant particles. One source of contaminant particles is undesirable species of ions generated in the ion source. Contaminant particles with respect to a given implant result from the presence of residual ions from a previous implant in which different ions were implanted. For example, after implanting boron ions in a given number of wafers, it may be desired to change over the implanter to implant arsenic ions. It is likely that some residual boron atoms remain in the interior region of the implanter.
Yet another source of contaminant particles is photoresist material. Photoresist material is coated on wafer surfaces prior to implantation and is required to define circuitry on the completed integrated circuit. As ions strike the wafer surface, particles of photoresist coating are dislodged from the wafer.
Contaminant particles which collide with and adhere to wafers during ion treatment are a major source of yield loss in the fabrication of semiconductor and other devices which require submicroscopic pattern definition on the treated wafers.
U.S. Pat. No. 5,656,092 to Blake et al concerns a method of capturing and removing contaminant particles moving within an evacuated interior region of an ion beam implanter is disclosed. A particle collector has a surface to which contaminant particles readily adhere. The particle collector is secured to the implanter such that particle adhering surface is in fluid communication to the contaminant particles moving within the interior region. At periodic intervals the particle collector is removed from the implanter.